The compositions which have found practical use as vaginal contraceptives typically incorporate an active ingredient which is spermicidal in effect. In spite of their high spermicidal activity, however, vaginal contraceptives incorporating these materials are not as effective in preventing conception as would be desirable. In addition, there are some indications that these materials possess undesirable side-effects.
In accordance with the invention, there is provided a method for inhibiting conception in mammals in which the contraceptive effects are achieved, not by immobilizing spermatozoa, as in the case of spermicidal contraceptives heretofore known, but by preventing the fusion of spermatozoa with ova by inhibiting one or more of the sperm enzymes necessary for this process, i.e., by functioning as enzyme inhibitors. It has been found that certain compounds, hereinafter described, function as inhibitors of sperm acrosin and possibly other enzymes and have high contraceptive potency when used vaginally in mammals, in a concentration sufficient to prevent fusion of ova and spermatozoa in the presence of the inhibitor.